1. Technical Field
The present invention relates to a surface acoustic wave device provided with an IC region and a surface acoustic wave element region on a semiconductor substrate to form a single chip.
2. Related Art
Surface acoustic wave devices represented by a SAW resonator or a SAW filter have various superior characteristics such as high frequency, compact size, or high mass productivity, and therefore, are widely used in the telecommunications field. In recent years, along with the popularization of mobile telecommunication devices, downsizing and weight saving of components used in the high-frequency area are strongly desired.
To cope with the desire, as shown in a document of J. H. Viseer, IEEE, Ultrasonics Symposium, p.195-200 (1989), for example, there is proposed a surface acoustic wave device having a SAW filter formed by providing a piezoelectric thin film on a semiconductor substrate partially provided with a high-frequency amplifier circuit or the like instead of using a surface acoustic wave element as a filter unit.
In such a surface acoustic wave device equipped with an IC region and a surface acoustic wave region on a semiconductor substrate to form a single chip, semiconductor elements and wiring for connecting the semiconductor elements are formed via an insulating film as a multi-layered structure in the IC region. Since, in contrast, only the insulating film is stacked in the surface acoustic wave element region, a step is created between the IC region and the surface acoustic wave element region. Typically, in case of such a surface acoustic wave device, a large number of surface acoustic wave devices are formed in a semiconductor wafer so as to border on each other, and as layers such as the insulating layer are stacked, the step inclines and advances to the surface acoustic wave element region, this causes a problem that the flatness of the surface of the surface acoustic wave element region cannot be assured. If the flatness of the surface is not sufficient, the surface acoustic wave element cannot be manufactured with sufficient dimensional accuracy, which degrades the performance of the surface acoustic wave element. Further, the unevenness of the surface caused by the insufficient flatness causes a variation in the thickness of the piezoelectric thin film formed thereon, and a variation in the resonant frequency of the surface acoustic wave element is concerned.